Basic zinc chloride, with a molecular formula of ZnCl2.4Zn(OH)2.H2O (or Zn5(OH)8Cl2.H2O), has good biological effects and adaptability. When being mixed with food, basic zinc chloride does not react with other ingredients, and basic zinc chloride is an excellent micronutrient additive and is mostly likely to replace other inorganic zinc such as zinc sulfate and zinc oxide. Moreover, basic zinc chloride has similar biological properties to the organic zinc, but its market price is lower; therefore, and the market prospect of basic zinc chloride is extensive.
In the international market, particularly in the European market, in addition to strict control over chemical indexes of basic zinc chloride, such as Pb, Cd, As, Hg and fluorine, there are also very strict requirements on the physical index—particle size—of basic zinc chloride. When the particle size is too large, the mixing dispersibility of the basic zinc chloride with other ingredients is poor; and when the particle size is small, dust is raised easily, thus producing an adverse effect on the environment and the human body.
There are many basic zinc chloride synthesis methods. However, these methods are roughly classified into two categories: (1) a zinc oxide method and (2) a hydrochloric acid or zinc chloride method. According to the zinc oxide method, basic zinc chloride is prepared by adopting alkali or alkali compounds and zinc oxide as raw materials, e.g., strong alkali or ammonia water is used in an embodiment of the patent CN101712485B METHOD FOR PREPARING BASIC ZINC CHLORIDE; and in the patent CN100496278C METHOD FOR PREPARING BASIC ZINC CHLORIDE FEED ADDITIVE and the patent CN1328171C METHOD FOR PREPARING MICROELEMENT ADDITIVE BASIC ZINC CHLORIDE, crushed Zn and ZnCl2 are used as zinc sources respectively to be synthesized with zinc oxide to form basic zinc chloride. According to the hydrochloric acid or zinc chloride method, basic zinc chloride is formed by causing zinc-containing alkali compounds to react with hydrochloric acid or zinc chloride under appropriate conditions, concrete zinc compounds are ZnO, Zn(OH)2 and basic zinc carbonate and the like, and this method is adopted in, e.g., patents CN100564263 and CN100366539C.
As can be seen from the implementation process, the liquid-solid phase heterogeneous reaction generally occurs in the foregoing patents, the operation process is complex, generated basic zinc chloride is easily adsorbed to the surfaces of raw materials to form coating or sandwiching, and chemical ingredients of the product are determined by the raw materials completely, so that the quality is difficult to guarantee. Moreover, basic zinc chloride prepared in the foregoing process is large in specific surface area, so that the basic zinc chloride is high in water content and poor in filtering and washing performance and needs to undergo centrifugal dewatering, equipment and operations are complex, the fixed investment is high, the drying energy consumption is also high, and the industrialization cost is high.
A homogeneous phase synthetic route of using zinc chloride solution and ammonia water is put forward in the patent CN1027457378 METHOD FOR SYNTHESIZING BASIC ZINC CHLORIDE SINGLE-CRYSTALLINE NANOROD, and the chemical indexes of a product can be guaranteed by adopting appropriate control means. However, the content of zinc chloride used in the invention is low (0.08-0.16 mol/L), synthesized basic zinc chloride particles are small (the diameters are 70.0 nm and the lengths are about 400 nm); absolute ethyl alcohol is used for dewatering and drying, the investment of synthesis, separation and drying equipment needed for mass production is high, the running cost is high, the product has difficulty in meeting the market demand, and thus the industrialization prospect is not ideal.